Initially, de Havilland concentrated on single and two-seat biplanes, essentially continuing the DH line of aircraft built by Airco, but powered by de Havilland's own Gipsy engines. These included the Gipsy and Tiger Moths. These aircraft set many aviation records, many piloted by de Havilland himself. Amy Johnson flew solo from England to Australia in a Gipsy Moth in 1930.

The Moth line of aircraft continued with the more refined (and enclosed) Hornet Moth and Moth Minor, the latter being a low-wing monoplane constructed of wood. One of de Havilland's trademarks was that the name of the aircraft type was painted on using a particularly elegant Roman typeface, all in capital letters. When there was a strike at the plant, the artisans who painted the name on the planes used the same typeface to make the workers' protest signs.

The DH 84 Dragon was the first aircraft purchased by Aer Lingus, who later operated the DH 86B Dragon Express and the DH 89 Dragon Rapide. De Havilland continued to produce high-performance aircraft including the high-speed twin-piston-engine DH 88 Comet mail plane, one of which became famous in its red livery as the winner of the MacRobertson Air Race from England to Australia in 1934.

The high-performance designs and wooden construction methods culminated in perhaps the most famous de Havilland aircraft—the Mosquito, constructed primarily of wood because of the shortage of aluminium during the Second World War. The company followed this with the even higher-performing Hornet, which was one of the pioneers of the use of metal-wood and metal-metal bonding techniques.

After the Second World War, de Havilland continued with leading-edge designs in both the military and civil field, but several public disasters doomed the company as an independent entity. The experimental, tailless, jet-powered de Havilland DH 108 Swallow crashed in the Thames Estuary, killing Geoffrey de Havilland Jr, son of the company's founder. A large additional aircraft factory was acquired in 1948 at Hawarden Airport at Broughton near Chester where production supplemented the Hatfield output. The de Havilland Comet was put into service in 1952 as the eagerly-anticipated first commercial jet airliner, twice as fast as previous alternatives and a source of British national pride. The Comet suffered three tragic and high-profile crashes in two years. Less well remembered, but equally disastrous, was the in-flight break up of the DH 110 prototype during the 1952 Farnborough Airshow, which also killed members of the public.

Following the structural problems of the aircraft in 1954, all remaining Comets were withdrawn from service, with de Havilland launching a major effort to build a new version that would be both larger and stronger. This one, the Comet 4, enabled the de Havilland airliner to return to the skies in 1958. By then, the United States had its Boeing 707 jetliner along with the Douglas DC-8, both of which were faster and more economical to operate. Orders for the Comet dried up.

Hawker Siddeley bought de Havilland in 1960 but kept it as a separate company until 1963. In that year it became the de Havilland Division of Hawker Siddeley Aviation and all types in production or development changed their designations from "DH' to "HS" (see Hawker Siddeley Trident and BAe 125). The famous "DH" and the de Havilland name live on, with several hundred Moths of various types and substantial numbers of many of the company's other designs still flying all over the world.

De Havilland returned to the airline world in 1962 with a three-engine jetliner, the DH 121 Trident. However, the design was modified to be smaller to fit the needs of one airline and one man: MRAF Sholto Douglas later Lord Douglas of Kirtleside, chairman of British European Airways. Other airlines found it unattractive and turned to a rival tri-jet: the Boeing 727 which was much the same size as the original DH 121. De Havilland built only 117 Tridents, while Boeing went on to sell over 1,800 727s.

De Havilland also pushed into the new field of long-range missiles, developing the liquid-fuelled Blue Streak. It did not enter military service but became the first stage of Europa, a launch vehicle for use in space flight. In flight tests, the Blue Streak performed well—but the upper stages, built in France and Germany, repeatedly failed. In 1973, the Europa programme was cancelled, with Blue Streak dying as well. The last of them wound up in the hands of a farmer who used its fuel tanks to house his chickens. 

Source: Wikipedia